COMPARISON OF SHIPS HEADING DETERMINED FROM AN ARRAY OF GPS ANTENNAS WITH HEADING FROM CONVENTIONAL GYROCOMPASS MEASUREMENTS

An Ashtech GPS 3DF, a commercially available system for measuring ship's heading from an array of GPS antennas, was installed on RRS Discovery in August 1992. Data were collected during 8 days of ship trials, including periods in port and while on station or steaming. Headings from the GPS system have been compared with headings from the ship's gyrocompass, and residuals calculated. While in port, residuals had a standard deviation of 0.066 degrees, suggesting satisfactory performance by both instruments. While at sea, time-averaged residuals varied with a range of nearly 3 degrees, most of which is attributed to systematic errors in the ship's gyro. After correcting the gyro using 10-min averages of the GPS minus gyro headings, the residual GPS minus gyro differences had a standard deviation of 0.17 degrees. This represents a likely limit on the use of GPS heading data to improve conventional gyro measurements.